Charlie Murder

Contrary to the other solutions the quickest place to get this is in Gor'Castle Parks entrance (Credit to Das Chase on this). Take the boat ride, and skip the cut scene by pressing Y. Go to the right until enemies spawn, hopefully you get one or two machete guys, if you only get 1 machete go back left and then return right and magically enemies will respawn for you. Once you get two machetes proceed with the limb hacking (focus on the fat kids, machete, and chainsaw dudes) until the achievement pops. I cannot verify if this is progressive or if it has to be done in one go, by the way mine popped I would assume it is progressive but don't quote me on that.

If you have put some wear and tear on your machetes you can always go left one screen and then return, it heals your weapons so you don't have to spawn machete dudes again.

IMPORTANT NOTE: This WOULD NOT unlock for me as the guest in a coop game, we tried for about an hour and I quit in frustration. Once I vented long enough I played to that point in single player and it popped in my first attempt. Good luck.

Everyone's Solution is good. Just wanted to add a Video showing how I got this achievement. I've noticed that it Takes a while for this achievement to work. Done it a few times before this and didn't unlock, so just keep trying and it will eventually pop.

As Charlie, walk from Needle Beach to Hermit's Refuge Cave. There should be some guys with machetes that spawn. Make sure you equip two machetes and kill all the mobs that remain. This popped for me when I killed the final enemy in the area outside the cave.

first you Need to be Charlie and unlock the dual melee weapon skill..... then go form needle beach to hermit's refuge. the enemies that carry them are guys with ski masks and wife beaters on.... they look like Jason Vorhees. knock the weapons out of their hands and pick them up.... now I've noticed they break pretty fast so i softened up the enemies with a scream move then i hit them the machetes. took me a few tries but it worked.

Just to add to other solutions, I did this on Gor Castle Park, right after the boat ride. You wanna look for the guys who look like Jason Vorhees. When you see them, try to beat them up so they drop the weapon. Don't pick it up. Take care of the other guys, and don't let them pick up that weapon. Once you are done with them, if you managed to pick up 2 machetes, go back to the left. This will heal your weapons. If you only got one, go left and then go back right and throw the weapon to the first enemy, and again try to beat them all up. You should get a second machete this time.

Once you got 2 machetes, go back left, then come back right. This will spawn more enemies. As soon as you see them coming, use the Frozen Vocals magic to take down some of their health, then start hacking. It may not work the first time.

Things I've discovered: you have to sever a limb. Not just kill them. I tried the Cyclone while dual wielding with but didn't work. I killed about 7 guys that way, but none of them got severed. I tried beating enemies and killed about 6, no severed limbs. When I did the Frozen magic, that's when I finally severed one of Jason's arms and it popped. Not sure if it was my first severed limb or what, but that's how it popped.